The invention relates to line following systems, and deals more particularly with a line following system utilizing an optical scanning device to generate matrix representations of portions of a line being followed and a computing means for analyzing information contained in said matrix representations to direct the movement of the optical scanning device along the course of the line and to make a digital representation of the line.
Line followers are frequently used to digitize design drawings of automobiles, mechanical structures, or other objects which have features subject to creative design. Although these designs may originate from the efforts of a person drawing with a mechanical drafting instrument on a sheet of paper, it is a common practice in the design of objects such as described above for the hand-written drawings to be translated into computer language, stored in a computer, made available for display on a monitor, and from then on, be subject to additions and alterations in the course of a redesign of the object. Such a redesigning process, sometimes called computer aided design, is especially advantageous when changes are required for a relatively small portion of the drawing in which case, only that portion of the drawing need be redrafted. Without a computer aided design system, a draftsperson may be required to redraft the entire drawing, copying or tracing the unchanged sections and altering the section to be redesigned, this latter approach consuming much more time than the computer aided design one.
Also with a computer aided design system such as may utilize digital representations produced by the present invention of two or more views of an object, it may be possible, for a computer to generate a digital representation of another view of the object for displaying or editing purposes.
A line following system is disclosed in U.S. Pat. No. 3,529,084 to Rich in which system a vidicon tube produces a circular scan around a portion of a line being followed, and each time the scan crosses the line, the vidicon tube produces a pulse. If the circular scan is centered directly over a portion of the line, the vidicon tube will produce pulses which are equally spaced in time, and if the circular scan is centered somewhat off the line, the vidicon tube will produce pairs of pulses, which pulses of a given pair are spaced closer to one another than to a previous or subsequent pulse, the more off center the vidicon tube, the more the pulses of a given pair are separated from the previous or subsequent pulse. The pulsed output of the vidicon tube is applied to a pulse phase comparator which develops an error signal representative of the deviation of the temporal spacing of the pulses from an equally spaced configuration of a reference pulse train. The error signal is applied to a variable frequency oscillator which produces a correction signal which it sends to two coordinate drive motors. In response, the motors move the vidicon tube closer to and along the line.
There are also know systems for digitizing a graphic inscription such as typing on a page for a purpose of transmitting a digital representation of the inscription over a telephone line or other data communication line. One such system bears the trade name FAX and it is presumed that such a system does not "follow" particular typed letters or other graphic inscriptions on the page but rather scans across the page, row by row, and senses inscribed points or segments within each row. As the inscriptions are scanned, they are digitized in one form or other, and such digitizations may be transmitted over a telephone line by means of a modem. Such a system may utilize a form of digitization commonly known as Run-Length-Encoding in which every pixel of a given row is not digitized, but rather a series of "run" numbers and "length" numbers are used to digitize inscriptions within or crossing each row. The run number indicates the number of blank pixels preceding a given mark or graphic inscription in the row and the length number indicates the length of the given mark or inscription within the row. For each scanned line, there are as many pairs of run and length numbers as there are distinct marks or graphic inscriptions in the row. The advantage of the Run-Length-Encoding system is that generally fewer bytes of digital information are needed to represent a graphic inscription on a page, and this savings shortens the time that is needed to transmit such a digital representation over a telephone line because telephone lines provide a relatively slow rate of data transfer. One or more systems of Run-Length-Encoding have also been developed in conjunction with research of a video telephone although the details are not presently known to the Applicants.
A general aim of the invention is to provide a line following system which can follow a line at a relatively high rate of speed and produce an accurate representation of the line.
Another general aim of the invention is to provide a line following system which is substantially automatic in operation.
A more specific aim of the invention is to provide a line following system which utilizes an optical scanning device to produce information corresponding to matrixes, each representing a portion of a line being followed.
Another specific aim of the invention is to provide a line following system which can follow a distorted line, one having small irregularities or gaps which may be caused by an appreciable age or usage of a sheet upon which the line is inscribed.
A still further aim of the invention is to provide a line following system which can negotiate relatively sharp turns of a line being followed without intervention by an operator.
Yet another aim of the invention is to provide a line following system in which selected portions of a graphic source material can be displayed on a monitor along with a representation of portions of the graphic source material which already have been followed and digitized, said representation being superimposed or otherwise indicated on the respective portions of the line.